Most people arrive at a surveyor because somebody else told them to get one: a lender, a title company, the county, or a neighbour with an opinion about where the fence goes. Whoever sent you usually named the survey they want, and the names are not obvious from the outside.
A boundary survey
The licensed work of establishing where your property lines actually run, and marking them on the ground. The surveyor researches the deed and the records, measures what is there, reconciles the two, and sets or recovers the monuments that mark the corners.
This is what you want when you are putting up a fence, building near a line, splitting a parcel, or settling a disagreement about where the boundary is. It is the answer to "where does my land end".
An improvement location report
A lighter product that shows where the buildings and improvements sit relative to the boundary. It is usually what a lender or title company asks for on a residential purchase, and it is cheaper and faster than a full boundary survey because it is answering a narrower question.
It is not a substitute for a boundary survey. If you need corners marked so you can build to them, ask for the boundary survey, whatever the lender called it.
An ALTA/NSPS land title survey
The detailed standard for commercial real estate transactions, ordered by a title company or a lender rather than by the owner. It reconciles the boundary against the title commitment and its exceptions, and the client picks optional items from a menu called Table A.
It is the most thorough and the most expensive of the three, and you will normally know if you need one because a transaction is requiring it. More on what an ALTA survey involves.
A FEMA elevation certificate
Not a boundary product at all. It records the elevation of a structure relative to the flood zone, and it exists for flood insurance. If your insurer or your community floodplain administrator asked for one, that is the document they mean.
If you are not sure, say what you are trying to do
Surveyors field this question every day. Telling a firm "I am buying this place and the lender wants something" or "I want to fence the back line" gets you to the right product faster than guessing at the name. Every quote request through this directory asks what you are trying to accomplish for exactly that reason.